A number of implantable drug delivery devices have been suggested to be capable of delivering the drug to the body lumen. One universal advantage to implanted drug delivery devices is related to the local administration of a drug that inherently improves efficacy and decreases side effects, when compared to other routes of administration such as oral, rectal, topical, or systemic.
Nonetheless, a problem with the known implantable drug delivery devices is that the delivery rate cannot be controlled during all operational phases of the devices (i.e., drug delivery rates may change thereby resulting in, for example, first order delivery kinetics or second order delivery kinetics). Such problems result in a drug delivery device that administers drugs in an unpredictable pattern, thereby resulting in poor therapeutic benefit.
For example, a popular drug delivery device is a drug eluting stent. Stents are mesh-like steel or plastic tubes that are used to open up a clogged atherosclerotic coronary artery or a blood vessel undergoing stenosis. A drug may be attached onto, or impregnated into, the stent that is believed to prevent re-clogging or restenosis a blood vessel. However, the initial release of the drug may be very rapid releasing 20-40% of the total drug in a single day. Such high concentrations of the drug have been reported to result in cytotoxicity at the targeted site.
As a result of these problems, there is a need for a drug delivery device, which can be optimized to deliver any therapeutic, diagnostic, or prophylactic agent for any time period up to several years maintaining a controlled and desired rate.